Substrate support device

ABSTRACT

A substrate support device formed of a metal and having a high withstand voltage and a high thermal resistance is provided. A substrate support device according to the present invention includes a plate section formed of a metal; a shaft section connected to the plate section and formed of a metal; a heating element provided in the plate section; and an insulating film formed on a first surface of the plate section, the first surface opposite to the shaft section, by ceramic thermal spraying. The substrate support device may further include an insulating film formed on a second surface of the plate section which intersects the first surface of the plate section approximately perpendicularly.

FIELD

The present invention relates to a substrate support device usable forproducing a semiconductor device, and specifically to a metal substratesupport device having a built-in heating element.

BACKGROUND

In production of a semiconductor device, specifically in processingsteps of chemical vapor deposition (CVD), surface reforming and thelike, a substrate support device is provided in a semiconductorproduction apparatus. In the case where the substrate support device isused in the state of being heated, a substrate support device having abuilt-in heating element is provided in the semiconductor productionapparatus. Such a substrate support device has a structure in which aplate formed of a metal or ceramic material is supported by a shaft.There are cases where a plasma electrode or a heating element isprovided in the plate and is connected to a control device providedoutside the semiconductor production apparatus via a line provided inthe shaft.

For a plate of such a substrate support device, bulk ceramics such asaluminum nitride (AlN), aluminum oxide (Al₂O₃) and the like are oftenused. However, in order to provide a plasma electrode or a heatingelement in the substrate support device, the inside of the plate needsto have a complicated structure. It is difficult to process bulkceramics into such a complicated structure. By contrast, a metal plateallows a complicated structure to be formed therein easily, and also atlower cost than bulk ceramics. In the case where a metal plate is used,a surface of the metal plate on which a substrate is to be mounted needsto be covered with an insulating material, and contamination of thesubstrate with metal caused by contact needs to be reduced. For example,Japanese Laid-Open Patent Publication No. 2007-184289 describes a metalplate which is given an alumite treatment (an anodizing).

However, when a metal plate is anodized, the anodized film has athickness of about 50 to 75 μm and a withstand voltage of about 0.8 to 1kV. It is difficult to realize a higher withstand voltage. For producinga precision semiconductor device of, for example, the 25 nm process orthe like, the metal plate needs to be covered with a material having ahigh thermal resistance in order to prevent the metal from beingcontaminated.

The present invention for solving the above-described problems has anobject of providing a substrate support device formed of a metal andhaving a high withstand voltage and a high thermal resistance.

SUMMARY

An embodiment of the present invention provides a substrate supportdevice comprising a plate section formed of a metal; a shaft sectionconnected to the plate section and formed of a metal; a heating elementprovided in the plate section; and an insulating film formed on a firstsurface of the plate section, the first surface opposite to the shaftsection, by ceramic thermal spraying.

The substrate support device may further comprise an insulating filmformed on a second surface of the plate section which intersects thefirst surface of the plate section approximately perpendicularly.

In the substrate support device, the second surface of the plate sectionmay have a portion having a curvature, having a value nearly equal to athickness of the plate section, which is curved outward toward a thirdsurface of the plate section, the third surface being connected to theshaft section.

In the substrate support device, the third surface may have an insultingfilm formed thereon.

In the substrate support device, the first surface of the plate sectionmay have a recessed portion; and an edge between the recessed portionand a peripheral non-recessed portion of the first surface, and an edgebetween the first surface and the second surface, may each have acurvature.

According to the present invention, a metal substrate support devicehaving a high withstand voltage and a high thermal resistance can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a substrate support device 100 accordingto an embodiment of the present invention;

FIG. 2 is a cross-sectional view of the substrate support device 100according to the embodiment of the present invention taken along lineA-A′ in FIG. 1; and

FIG. 3 is a cross-sectional view of a substrate support device 200according to an embodiment of the present invention taken along a linecorresponding to line A-A′ in FIG. 1.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a substrate support device according to an embodiment ofthe present invention will be described with reference to the drawings.The following embodiment is directed to an example of substrate supportdevice according to the present invention, and the substrate supportdevice according to the present invention is not limited to thefollowing embodiment.

With a thickness of an anodized film, it is difficult to provide a metalplate with a sufficiently high withstand voltage. Therefore, the presentinventors made researches to find a method for forming a ceramic film ona metal plate, which can realize a higher withstand voltage. One methodfor forming an insulating ceramic film on a metal plate is ceramicthermal spraying. With this method, a high withstand voltage can berealized but the resultant ceramic layer is cracked under a hightemperature condition and as a result, the plate is corroded or arcdischarge occurs between the plate and the substrate. For this reason,it is difficult to improve the yield of semiconductor devices.Accordingly, it is difficult to realize a high withstand voltage and ahigh thermal resistance at the same time by merely performing ceramicthermal spraying with a low-fusing.

As a result of conducting active studies on these problems, the presentinventors have found that by forming a thinnest possible insulating filmin the range in which a desired withstand voltage can be realized, asubstrate support device which is not cracked even under a hightemperature condition can be provided.

Embodiment 1

FIG. 1 is a perspective view of a substrate support device 100 accordingto an embodiment of the present invention. FIG. 2 is a cross-sectionalview of FIG. 1 taken along line A-A′ in FIG. 1. The substrate supportdevice 100 in this embodiment includes a plate section 110, a shaftsection 150, and a heating element 120 provided in the plate section110. A top surface of the plate section 110 has a recessed portion 113for supporting a substrate. The shaft section 150 is connected to acentral part of a rear surface, of the plate section 110, opposite tothe top surface having the recessed portion 113. The shaft section 150has a hollow structure 170. In the hollow structure 170 of the shaftsection 150, a line 160 connected to the heating element 160 and also toa control device (not shown) outside the substrate support device 100 isprovided.

The substrate support device 100 includes an insulating film 119 formedon the surface 113 of the plate section 110 for supporting the substrateand also on a side surface of the plate section 110. The top surface andthe side surface of the plate section 110 intersect each otherapproximately perpendicularly, and the side surface of the plate section110 has a portion having a curvature which is curved outward toward aconnection position on the rear surface of the plate section 110, atwhich the plate section 110 is connected to the shaft section 150. Inthe plate section 110, an edge between the recessed portion 113 and aperipheral non-recessed portion of the top surface, and an edge betweenthe top surface and the side surface, are rounded off so as to curvedoutward with a curvature.

The plate section 110 and the shaft section 150 in this embodiment areformed of a metal. A metal to be used can be selected from materialsknown as being usable for producing substrate support devices. Usablemetals include, for example, aluminum, stainless steel, copper, nickel,titanium and the like. The plate section 110 includes two components 110a and 110 b. A groove is formed in either the component 110 a or 110 b,and the heating element 120 is located in the groove. The components 110a and 110 b are joined together by soldering or welding.

By forming the plate section 110 and the shaft section 150 of a metal, acoolant flow path 190 shown in FIG. 2 may be formed in the shaft section150. The coolant flow path 190 is a mechanism for allowing a gas such asair or the like or a liquid such as oil, an aqueous solution of ethyleneglycol or the like to circulate to assist the shaft section 150 inadjusting the temperature of a heater. Such a complicated structurecannot be easily formed when the shaft section is formed of a ceramicmaterial, but can be formed in the shaft section 150 by soldering orwelding since the shaft section 150 is formed of a metal. This mechanismprovides higher-level temperature adjustment means. In addition, theabove-mentioned rounding can be conducted easily when the plate section110 is formed of a metal.

According to the present invention, the insulating film 119 is formed byceramic thermal spraying. When ceramic thermal spraying is used, it ispossible to form the insulating film 119 to be thicker than an anodizedfilm. However, when the insulating film 119 is made thicker by ceramicthermal spraying, the insulating film 119 is cracked under a hightemperature condition. The insulating film 119 according to the presentinvention is formed to be as thin as possible in the range in which adesired withstand voltage can be realized. Accordingly, the thickness ofthe insulating film 119 is set to any value in accordance with arequired withstand voltage. The plate section 110, which is rounded asdescribed above, can suppress a stress from being concentrated on theedges of the insulating film 119 so that the insulating film 119 is noteasily cracked even under a high temperature condition.

The insulating film 119 in this embodiment can be formed of any knownmaterial which realizes a desired withstand voltage and can beceramic-thermal-sprayed. For example, as the material of the insulatingfilm 119, an oxide of at least one of alkaline earth metals, rare-earthmetals, Al, Ta and Si can be selected. Specifically, aluminum oxide(Al₂O₃), magnesium oxide (MgO), yttrium oxide (Y₂O₃) and the like areusable. According to the present invention, a combination of a metal andan insulating material which have a small difference in the coefficientof thermal expansion is used. When the difference in the coefficient ofthermal expansion is large between the plate section 110 and theinsulating film 119, the insulating film 119 is easily cracked under ahigh temperature condition. An example of combination of a metal and aninsulating material which have a small difference in the coefficient ofthermal expansion is a combination of aluminum (Al) and aluminum oxide.When the plate section 110 is formed of aluminum and the insulating film119 is formed of aluminum oxide, the insulating film 119 is not crackedeasily. In general, ceramics have properties weak against a tensilestress. It is considered that when the plate section 110 is formed ofaluminum, which is thermally expandable, the plate section 110 isexpanded along the insulating plate 119 under a high temperaturecondition and thus the insulating plate 119 is not cracked easily.

In this embodiment, it is preferable that the ceramic insulating film119 formed by ceramic thermal spraying has a stoichiometric compositionor a composition close thereto. When being formed of a stoichiometriccomposition or a composition close thereto, the insulating film 119 isnot cracked easily even under a high temperature condition. When theamount of oxygen in the ceramic film is significantly lower than that ofthe stoichiometric composition, the insulating film 119 is easilycracked and thus the substrate support device cannot exhibit asufficiently high withstand voltage. By contrast, when the amount ofoxygen in the ceramic film is significantly higher than that of thestoichiometric composition, the adhesiveness of the insulating film 119to the plate section 110 is lowered, which is not preferable.

For ceramic thermal spraying conducted to form the insulating film 119in this embodiment, oxygen gas or oxygen-containing gas is used asplasma working gas. By using oxygen gas or oxygen-containing gas asplasma working gas, the composition of the insulating film 119 formed byceramic thermal spraying can be made closer to the stoichiometriccomposition than the composition of a film formed by conventionalthermal spraying. Thus, a high electrical insulating property and a highcorrosion resistance can be realized at the same time.

For forming the insulating film 119 in this embodiment, athermal-sprayed film having a larger thickness than the thickness atwhich a desirable withstand voltage can be realized is formed by ceramicthermal spraying. Then, the thermal-sprayed film is processed withsurface polishing to obtain the desired thickness. In this embodiment,it is preferable that the ceramic thermal spraying is performed in atleast two directions, i.e., a direction toward the top surface of theplate section 110 and a direction toward the side surface thereof. Inorder to provide the surface of the plate section 110 with theinsulating property without fail to prevent the metal from beingcontaminated, the insulating film 119 is formed on two surfaces, i.e.,the top surface and the side surface. As described above, in thisembodiment, the side surface of the plate section 110 has a portionhaving a curvature which is curved outward toward the connectionposition with the shaft section 150 on the rear surface. Therefore, onthe side surface of the plate section 110, the insulating film 119 isformed to be gradually thinner toward the connection position with theshaft section 150 on the rear surface, and thus the insulating film 119is not easily delaminated from the plate section 110.

In this embodiment, for the purpose of reducing stress concentration, itis desirable that the curvature (R value) of the portion of the sidesurface which is curved outward toward the connection position with theshaft section 150 is large. In this embodiment, it is preferable thatthis curvature is nearly equal to the thickness of the plate section110. Owing to this, the insulating film 110 can be formed to begradually thinner from the side surface of the plate section 110 towardthe connection position with the shaft section 150 on the rear surface,by thermal spraying conducted from a position to the side of the platesection 110.

The substrate support device 100 in this embodiment may include a bufferlayer, for alleviating the difference in the withstand voltage, formedbetween the plate section 110 and the insulating film 119. For thebuffer layer in this embodiment, magnesium oxide (MgO), for example, isusable.

Where the coefficient of thermal expansion of the plate section 110 isα_(s), the coefficient of thermal expansion of the insulating film 119is α_(f), the working temperature during the thermal spraying is T₀, theroom temperature is T₁, the temperature of the heater in use is T₂, andthe Young's modulus of the insulating film 119 is E, the thermal stressσ generated in the insulating film 119 is represented by the followingexpressions in the case where the thickness of the plate section 100 issignificantly larger than the thickness of the insulating film 119.During cold working: σ=(α_(s)−α₁)·E·(T ₀ −T ₁)During hot working: σ=(α_(s)−α₁)·E·(T ₀ −T ₂)

During cold working, (T₀−T₁) has a positive value, and becauseα_(s)>α_(f), has a positive value and the insulating film 119 receives acompressive stress. However, when the substrate support device 100 isused in the state of being heated at a temperature exceeding thetemperature of the plate section 110 used during the thermal spraying, σhas a negative value and the insulating film 119 receives a tensilestress, which causes cracks. The generation of the tensile stress insuch a temperature range or the vicinity thereof can be suppressed by,for example, setting the working temperature during the thermal sprayingto a range of 150° C. or higher and 200° C. or lower.

As described above, a substrate support device according to the presentinvention can be processed in a complicated manner because the platesection and the shaft section are formed of a metal, and is not easilycracked even under a high temperature condition and thus can realize ahigh withstand voltage because a thin insulating film is formed on theplate section by ceramic thermal spraying.

Embodiment 2

FIG. 3 is a cross-sectional view of a substrate support device 200according to an embodiment of the present invention taken along a linecorresponding to line A-A′ in FIG. 1. The substrate support device 200in this embodiment comprises a plate section 210 including threecomponents 210 a, 210 b and 210 c instead of the plate section 110. Theheating element 120 is provided in a groove formed in the component 210a or 210 b. The component 210 b or 210 c has a groove formed therein,which is used as a coolant flow path 290. A top surface of the platesection 210 has a recessed portion 213 for supporting a substrate, and ashaft section 150 is connected to a central part of a rear surface, ofthe plate section 210, opposite to the top surface having the recessedportion 213. The shaft section 150 is substantially the same as thatdescribed in Embodiment 1 and therefore will not be described in detail.

The substrate support device 200 includes an insulating film 219 formedon the surface 213 of the plate section 210 for supporting thesubstrate, on a side surface of the plate section 210, and on the rearsurface of the plate section 210 which is connected to the shaft section150. The top surface and the side surface of the plate section 210, andthe side surface and the rear surface thereof, intersect each otherapproximately perpendicularly. An edge between the top surface and theside surface, and an edge between the side surface and the rear surface,are rounded off so as to be curve outward with a curvature. An edgebetween the recessed portion 213 and a peripheral non-recessed portionof the top surface of the plate section 210 is rounded off to be curvedoutward with a curvature.

The plate section 210 and the shaft section 150 in this embodiment areformed of a metal. Usable metals are described in Embodiment 1 and willnot be described in detail. By forming the plate section 210 and theshaft section 150 of a metal, the components 210 a, 210 b and 210 c canbe joined together by soldering or welding, and also the plate section210 and the shaft section 150 can be joined together by soldering orwelding.

The coolant flow path 290 is a mechanism for assisting the adjustment ofthe temperature of a heater. As long as the temperature of the heatercan be efficiently adjusted, the coolant flow path 290 may be located inthe same manner as the heating element 120, or spirally, in the platesection 210. Such a complicated structure cannot be easily formed whenthe plate section is formed of a ceramic material, but can be formed inthe plate section 210 since the plate section 210 is formed of a metal.This mechanism provides higher-level temperature adjustment means. Inaddition, the above-mentioned rounding can be conducted easily when theplate section 210 is formed of a metal.

According to the present invention, the insulating film 219 is formed byceramic thermal spraying. The insulating film 219 according to thepresent invention is formed to be as thin as possible in the range inwhich a desired withstand voltage can be realized. Accordingly, thethickness of the insulating film 219 is set to any value in accordancewith a required withstand voltage. The plate section 210, which isrounded as described above, can suppress a stress from beingconcentrated on the edges of the insulating film 219 so that theinsulating film 219 is not easily cracked even under a high temperaturecondition.

The insulating film 219 in this embodiment can be formed of any materialwhich realizes a desired withstand voltage and can beceramic-thermal-sprayed. Usable metals are described in Embodiment 1 andwill not be described in detail. As described above, in this embodiment,it is preferable that the ceramic insulating film 219 formed by ceramicthermal spraying has a stoichiometric composition or a composition closethereto. When being formed of a stoichiometric composition or acomposition close thereto, the insulating film 219 is not cracked easilyeven under a high temperature condition.

For ceramic thermal spraying conducted to form the insulating film 219in this embodiment, oxygen gas or oxygen-containing gas is used asplasma working gas. By using oxygen gas or oxygen-containing gas is usedas plasma working gas, the composition of the insulating film 219 formedby ceramic thermal spraying can be made closer to the stoichiometriccomposition than the composition of a film formed by conventionalthermal spraying. Thus, a high electrical insulating property and a highcorrosion resistance can be realized at the same time.

For forming the insulating film 219 in this embodiment, athermal-sprayed film having a larger thickness than the thickness atwhich a desirable withstand voltage can be realized is formed by ceramicthermal spraying. Then, the thermal-sprayed film is processed withsurface polishing to obtain the desired thickness. In this embodiment,it is preferable that the ceramic thermal spraying is performed in threedirections, i.e., a direction toward the top surface of the platesection 210, a direction toward the side surface thereof, and adirection toward the rear surface thereof. The side surface of the platesection 210 in this embodiment may be processed to have a portion havinga curvature which is curved outward toward the connection position withthe shaft section 150 on the rear surface as described above inEmbodiment 1, instead of having the edge between the side surface andthe rear surface. In this case, the formation of the insulating film 219on the rear surface of the plate section 210 may be omitted to simplifythe production process.

The substrate support device 200 in this embodiment may include a bufferlayer, for alleviating the difference in the withstand voltage, formedbetween the plate section 210 and the insulating film 219. For thebuffer layer in this embodiment, magnesium oxide (MgO), for example, isusable.

As described above, a substrate support device according to the presentinvention can be processed in a complicated manner because the platesection and the shaft section are formed of a metal, and is not easilycracked even under a high temperature condition and thus can realize ahigh withstand voltage because a thin insulating film is formed on theplate section by ceramic thermal spraying.

Examples

Hereinafter, an example of the substrate support device 100 according tothe present invention described above will be shown and described indetail.

In this example, the plate section 110 was formed of aluminum, and theinsulating film 119 was formed of aluminum oxide. For producing theinsulating film 119, ceramic thermal spraying was performed to form athermal-sprayed film having a thickness of 250 μm to 300 μm, and thenthe thermal-sprayed film was polished to have a thickness of 100 μm to150 μm.

Samples of the substrate support device 100 thus produced were heated at120° C., 150° C., 200° C. and 250° C. for 5 hours in an oven to inspectwhether the insulating film 119 of each sample was cracked or not. Inany of the samples, no crack was generated. The investigation resultsare summarized in Table 1.

TABLE 1 Thickness Dielectric strength (μm) Heated at 250° C. (2 kV DC)70.9 ◯ X 77.7 ◯ ◯ 84.7 ◯ X 84.8 ◯ ◯ 86.4 ◯ ◯ 86.7 ◯ X 88.1 ◯ X 91.1 ◯ ◯93.1 ◯ ◯ 97.1 ◯ ◯ 100.2 ◯ ◯ 105.3 ◯ ◯ 129.4 ◯ ◯ 137.3 ◯ ◯ 142.0 ◯ ◯144.0 ◯ ◯ 144.8 ◯ ◯ 154.7 ◯ ◯ 163.0 ◯ ◯ 164.9 ◯ ◯ 168.1 ◯ ◯ 168.5 ◯ ◯170.1 ◯ ◯ 300.0 X

By contrast, in the case where the post-polishing thickness of theinsulating film 119 was 300 μm or larger, cracks were generated. In adielectric strength test in which a DC voltage (DC) of 2 kV was appliedto the samples, the insulating film 119 was destroyed when the thicknessthereof was less than 90 μm. From these results, it has been found thatthe thickness of the insulating film 119 is preferably 100 μm or largerand 200 μm or less.

The invention claimed is:
 1. A substrate support device, comprising: aplate section formed of a metal; a shaft section connected to the platesection and formed of a metal; a heating element provided in the platesection; a first insulating film formed on a first surface of the platesection, the first surface opposite to the shaft section, by ceramicthermal spraying; and a second insulating film formed on a secondsurface of the plate section which intersects the first surface of theplate section approximately perpendicularly, by ceramic thermalspraying, wherein: the first surface of the plate section has a recessedportion; an edge between the recessed portion and a peripheralnon-recessed portion of the first surface has a curvature rounded off soas to be curved outward, and an edge between the first surface and thesecond surface has a curvature rounded off so as to be curved outward;the first and second insulating films are insulating films as thin aspossible in a range to achieve a desired withstand voltage; the secondsurface of the plate section has a portion having a curvature, andhaving a value nearly equal to a thickness of the plate section, whichis curved outward toward a third surface of the plate section, the thirdsurface being connected to the shaft section; the second insulating filmis gradually thinner from the second surface of the plate section towarda connection position with the shaft section on the third surface; andthe first insulating film connects the second insulating film on theedge between the first surface and the second surface, a connection partof the first insulating film and the second insulating film has acurvature rounded off so as to be curved outward.
 2. The substratesupport device according to claim 1, wherein the first and secondinsulating films are formed of a material being ceramic-thermal-sprayed,the material of the first and second insulating films is selected froman oxide of at least one of alkaline earth metals, rare-earth metals,Al, Ta and Si, a difference in the coefficient of thermal expansionbetween the plate section and the first and second insulating films issmall.
 3. The substrate support device according to claim 2, wherein thematerial of the first and second insulating films is selected fromaluminum oxide (Al₂O₃), magnesium oxide (MgO) and yttrium oxide (Y₂O₃).4. The substrate support device according to claim 3, wherein a materialof the plate section is aluminum (Al) and the material of the first andsecond insulating films is aluminum oxide.
 5. The substrate supportdevice according to claim 4, wherein the thickness of the first andsecond insulating films is 100 μm or larger and 200 μm or less.
 6. Thesubstrate support device according to claim 2, wherein the first andsecond insulating films formed by ceramic thermal spraying have astoichiometric composition or a composition close thereto.
 7. Thesubstrate support device according to claim 1, further comprising abuffer layer formed between the plate section and the first and secondinsulating films.
 8. The substrate support device according to claim 7,wherein the buffer layer is made of magnesium oxide (MgO).
 9. Asubstrate support device, comprising: a plate section formed of a metal;a shaft section connected to the plate section and formed of a metal; aheating element provided in the plate section; a first insulating filmformed on a first surface of the plate section, the first surfaceopposite to the shaft section, by ceramic thermal spraying; a secondinsulating film formed on a second surface of the plate section whichintersects the first surface of the plate section approximatelyperpendicularly, by ceramic thermal spraying; and a third insulatingfilm formed on a third surface of the plate section by ceramic thermalspraying, the third surface being connected to the shaft section,wherein: the first surface of the plate section has a recessed portion;an edge between the recessed portion and a peripheral non-recessedportion of the first surface has a curvature rounded off so as to becurved outward, an edge between the first surface and the second surfacehas a curvature rounded off so as to be curved outward and an edgebetween the second surface and the third surface has a curvature roundedoff so as to be curved outward; the first, second and third insulatingfilms are insulating films as thin as possible in a range to achieve adesired withstand voltage, the first insulating film connects the secondinsulating film on the edge between the first surface and the secondsurface a connection part of the first insulating film and the secondinsulating film has a curvature rounded off so as to be curved outward;and the second insulating film connects the third insulating film on theedge between the second surface and the third surface, a connection partof the second insulating film and the third insulating film has acurvature rounded off so as to be curved outward.
 10. The substratesupport device according to claim 9, wherein the first and secondinsulating films are formed of a material being ceramic-thermal-sprayed,the material of the first and second insulating films is selected froman oxide of at least one of alkaline earth metals, rare-earth metals,Al, Ta and Si, a difference in the coefficient of thermal expansionbetween the plate section and the first and second insulating films issmall.
 11. The substrate support device according to claim 10, whereinthe material of the first and second insulating films is selected fromaluminum oxide (Al₂O₃), magnesium oxide (MgO) and yttrium oxide (Y₂O₃).12. The substrate support device according to claim 11, wherein amaterial of the plate section is aluminum (Al) and the material of thefirst and second insulating films is aluminum oxide.
 13. The substratesupport device according to claim 12, wherein the thickness of the firstand second insulating films is 100 μm or larger and 200 μm or less. 14.The substrate support device according to claim 10, wherein the firstand second insulating films formed by ceramic thermal spraying have astoichiometric composition or a composition close thereto.
 15. Thesubstrate support device according to claim 9, further comprising abuffer layer formed between the plate section and the first and secondinsulating films.
 16. The substrate support device according to claim15, wherein the buffer layer is made of magnesium oxide (MgO).